tag inside tag beautifulsoup

html = """<div class="pr">
</div>
<li>
 <a href="pr/protocol">
  protocol
 </a>
 </li>"""

soup = BeautifulSoup(html, "lxml")

a = soup.select_one("div[class=pr]")

# Li parent
parent = soup.new_tag("li", class_="parent")
# Child anchor
child = soup.new_tag("a", href="hm/test", class_="child")
child.string = 'TEST'
# Append child to parent
parent.append(child)
# Insert parent
a.insert_after(parent)
print(soup.prettify())